Anodic bonding is a well known technique of bonding a silicon substrate to a glass substrate having a thermal expansion coefficient similar to that of a silicon substrate. A conventional method to form an anodic bonding structure 10 is described with reference to FIG. 1. A silicon substrate 12 is deposited typically on a lower electrode 13a, preferably made of brass and includes cartridge heaters. A glass substrate 14 is aligned on top of the silicon substrate 12. The glass substrate such as a Pyrex glass, i.e., Corning glass 7740, is generally used in an anodic bonding process includes predetermined amounts of sodium (Na) and potassium (K) so that when the Pyrex glass is heated at a temperature of over 200° C., elements are charged and easily moved by a voltage. An upper electrode 13b, also made of brass with cartridge heaters, is bonded to the glass substrate 14 with a graphite electrode 15 as shown in FIG. 1. When the silicon substrate 12 and the glass substrate 14 are aligned as shown, the two substrates are heated at a temperature of about 425° C. to form a bond between the silicon substrate 12 and the glass substrate 14. The substrates are heated via the upper and the lower electrodes 13a and 13b respectively. Then, a voltage of about 1 KV is applied for approximately two minutes to the substrates via a DC power supply 16, causing movable charges to move rapidly. Thus, strong dielectric charges occur on the interfaces of the silicon substrate 12 and the glass substrate 14 to initiate and complete the formation of the bond of the silicon substrate 12 with the glass substrate 14. A force 17 is applied to the structure 10 using any means such as the pneumatic piston or a spring loaded system. As shown in FIG. 1, the lower electrode 13a is preferably placed on a ceramic brick 18. The brick 18 provides thermal insulation between the electrode 13a (heater) and a base or table (not shown) where the bonding apparatus is positioned. A plurality of micro-electromechanical systems (MEMS) processes use an anodic bonding method that realizes a stable silicon structure.
U.S. Pat. No. 5,747,169 discloses a method of bonding a glass substrate and a nonconductive substrate using a field-assist bonding material preferably a non-doped silicon at low temperatures.